In recent years, we have taken a growing interest in health and it is known that excessive intake of salt injures our health. Accordingly, there have been proposed methods for relieving a decrease in saltiness due to the reduction in salt content. For example, JP-A-63-137658 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a method for enhancing the saltiness of a food comprising adding thaumatin in an amount of from 1/1,000 to 1/10,000 that of salt; JP-63-3766 proposes a method comprising adding collagen, which contains 1 to 4% by weight of a collagen hydrolysate and has a molecular weight of from 2,000 to 5,000, to a food at a ratio of 10% or below based on the whole food; and JP-A-2-53456 proposes a method comprising hydrolyzing a mixture of black koji-mold with yellow green koji-mold and adding the digested liquid thus obtained to a food.
However, the method described in JP-A-63-137658 has a disadvantage that thaumatin employed therein is a sweetener and, therefore, the ratio of this additive to salt is limited. Each of the methods described in JP-A-63-3766 and JP-A-2-53456 requires one to purify and fractionate the active components in order to eliminate an offensive taste and an offensive odor. In addition, the active components employed therein are in the form of a mixture. Namely, no single substance capable of enhancing saltiness is disclosed therein.
On the other hand, it has been required to conveniently provide drinking water, drinks and foods which are delicious and highly safe. However the inherent flavors of these products are frequently deteriorated due to processing or cooking treatments. Accordingly, there have been proposed methods for modifying tastes so as to give the original flavors of these drinks and foods.
Examples of methods for the production of widely usable substances having a full-bodied flavor include a method which comprises extracting root crops, eliminating aroma components from the extract and concentrating or drying the residue to thereby give a mixture containing a substance capable of imparting a full-bodied flavor (refer to JP-A-53-86068) and another method which comprises electrodialyzing molasses optionally together with cheese whey and concentrating or drying the electrolytic components to thereby give a mixture containing a substance capable of imparting a full-bodied flavor (refer to JP-A-61-216657). However, the substances giving a full-bodied flavor obtained by these methods have never been identified though they have been obtained in the form of a mixture. Namely, none of these inventions relates to a single substance capable of expressing a full-bodied flavor.
That is to say, there hats been known no saltiness-enhancing substance which not only enhances the expression of the saltiness of any food (for example, drinking water, drinks, foods) to thereby enable salt-reduction but also has composite functions of imparting or enhancing a full-bodied flavor through synergistic effects of a function of enhancing the saltiness with another function of modifying sourness, promoting the volatilization of aroma and preventing the deterioration in the flavor of the food due to oxidation to thereby activate the original flavor of the food.
Triose-reductone is contained in foods obtained from natural materials [Nogei Kagaku Kaishi, 46, 137-145 (1972)] and blackstrap molasses [Seito Gijutsu Kenkyu Kaishi, 22, 65-76 (1970)]. It is also formed-as an alkaline decomposition product from monosaccharides and polysaccharides [Adv. in Carbohydr. Chem. & Biochem., 46, 273-326 (1988)]. Even if this compound is contained as one of the components in the mixture as described in the above-mentioned JP-A-61-216657, its content therein is limited and it has a low titer. In addition, troublesome purifying procedures are needed in order to remove the offensive taste or odor and, furthermore, the compound is obtained at only a low yield. When the above-mentioned mixture contains various components in addition to this compound, in particular, said mixture is hardly usable in products which should not show any offensive taste or odor (for example, drinking water, drinks and fruit juice).
As the following formulae show, triose-reductone exists as a resonance hybrid (1), a cis-isomer (1-a) and a trans-isomer (1-b). Usually, it is in the form of the solid trans-isomer (1-b). In a solution, it exists as the trans-isomer (1-b) and the resonance hybrid (1) wherein hydroxymalondialdehyde forms an intramolecular hydrogen bond together with the cis-isomer (1-a). Namely, hydroxymalondialdehyde does not exist alone [F. Frimmel, H. P. Fritz, C. G. Kreiter, J. Cryst. Struct., 1, 25-32 (1971)]. Therefore, a hydroxyl group proton in the resonance hybrid (1) is equivalent in an aqueous solution [Obata and Tokuyama, Nippon Kagaku Zasshi, 91, 1098-1099 (1970)] and very easily dissociates to thereby give an acidity comparable to acetic acid. It forms mono- to trivalent salts together with metal ions [Beilsteins Handbunch der Organischem Chemie, EIV, 4146, ibid., EIII, 1, 3313].
Triose-reductone and hydroxymalondialdehyde represented by the following formula (2) and hydroxypyruvaldehyde represented by the following formula (3) are tautomers. Hydroxypyruvaldehyde exists either as a monomer or as a polymer. Triose-reductone is formed via an irreversible isomerization of hydroxypyruvaldehyde in the presence of an alkali and reduces silver, bromine and iodine ions in solutions [G. Hesse, F. Ramissch, K. Kennet, Ber., 89, 2143 (1956)]. ##STR1##
The most important point resides in that there have never been known the functions of the compound, which exists in the above-mentioned state in a solution, of modifying and enhancing the expression of the saltiness of drinking water, drinks or foods containing water, modifying sourness into a sharp taste just like umeboshi (plum pickles), imparting or enhancing the full-bodied flavor through synergistic effects of modifying both the saltiness and sourness and promoting the volatilization of an aroma.
The present inventors have previously found out that when monomers or polymers of .alpha.-hydroxyketone derivatives such as hydroxyacetaldehyde, glyceraldehyde, acetoin, acetol, 2-hydroxpropionaldehyde, 3,4-dihydroxy-2-butanone and 1,3-dihydroxyacetone are either singly or combinedly added either as such or as a solution to drinking water, a drink or a food containing water at a ratio of from 50 to 10,000 ng per gram of the food, the saltiness of the food is modified into a mild and full-bodied one while the sourness thereof is modified into a sharp and full-bodied one just like umeboshi. Thus they have found a novel flavor-modifying substance capable of imparting to a food and enhancing the full-bodied flavor of a food via synergistic effects of modifying the saltiness and sourness thereof. Further, they have developed a method for improving the flavor of a drink or a food by using said compound.
Subsequent studies have brought about the completion of the present invention. The compound according to the present invention not only maintains a preferable intensity of saltiness, even though the salt content of a food is reduced, but also imparts to and enhance the full-bodied flavor of the food, promotes the volatilization of the aroma thereof, prevents the deterioration in the flavor of the food and activates the original flavor of the food without injuring the original flavor of the food. Namely, it is a flavor-modifying substance having composite functions.
However, the above-mentioned compound is a highly unstable compound from the chemical viewpoint which is liable to undergo heat decomposition or oxidation with air, highly soluble in water and polymerized by heating under alkaline or acidic conditions [Beilstein Handbuch der Organischen Chemie, EIII, 1, 3310-3312]. Furthermore, it can hardly be analyzed and easily adsorbed by an ion exchange resin. Accordingly, it is unavoidable at present that the compound contained in foods obtained from natural substances such as underground water and fruit juice is reduced or lost with an increase in the number of processing or cooking procedures (for example, purification of drinking water with the use of ion exchange resins, extraction and concentration of various fruit juice or food materials, pasteurization of foods and drinks). As a result, its effect of expressing saltiness is deteriorated, which makes it necessary to increase the salt content of a food. Further, it is unavoidable at present that the flavor of the food is deteriorated thereby.
It is effective for human health to reduce the salt content in a food by enhancing the expression of saltiness. Thus there have been proposed a number of salt-reducing formulations and additives having an effect of reducing salt content. However, there has never been reported hitherto any compound which not only maintains a preferable intensity of saltiness of any food (for example, drinking water, drinks, fruit juices), even though the salt content of the food is reduced, but also imparts to and enhances the full-bodied flavor of the food, promotes the volatilization of the aroma thereof, prevents the deterioration in the flavor of the food and activates the original flavor of the food via synergistic effects of modifying the sourness and/or the saltiness without injuring the original flavor of the food, namely, a flavor-modifying substance having composite functions.
As described above, the compound according to the present invention is unstable to heat and air, highly soluble in water and exists in a complicated state in a solution. Although it is contained as a decomposition product of monosaccharides and polysaccharides in underground water, fruit juices and flavors and seasoning liquors obtained from natural materials, it is therefore unavoidable at present that the compound contained in foods is reduced or lost with an increase in the number of processing or cooking procedures (for example, cooking, pasteurization, purification with the use of ion exchange resins, solvent extraction, membrane concentration, distillation concentration, washing). As a result, its effect of expressing saltiness is deteriorated, which makes it necessary to increase the salt content of a food. Further, it is unavoidable at present that the flavor of the food is deteriorated thereby.
A flavor-modifying substance, whereby these problems can be solved, should be an odorless, single substance capable of modifying and enhancing saltiness, imparting to and modifying a full-bodied flavor and promoting the volatilization of an aroma without deteriorating the original flavor of the food by evolving any offensive odor or taste or injuring human health. However, publicly known substances capable of enhancing saltiness are frequently accompanied by offensive taste or odor, since some of the functions of sweeteners are utilized therefor or such substances are provided in the form of a mixture. On the other hand, publicly known substances capable of imparting a full-bodied flavor are provided not as a single substance but as a mixture. Thus, no single compound capable of expressing a full-bodied flavor has been identified so far. In addition, the titers of such substances are restricted by the starting materials, production methods and utilization methods. Further, a mixture frequently has an offensive taste or odor, which makes it hardly applicable to drinking water, drinks and fruit juices of the popular type.
A flavor obtained from a natural material and containing said compound as a constituent has a limited titer and an intense aroma which restricts the application range thereof as a general-purpose flavor-modifying substance.
That is to say, each of the publicly known saltiness-enhancing substances and full-bodied flavor-imparting ones mainly aims at enhancing saltiness or expressing a full-bodied flavor and none of them is a flavor-modifying substance capable of activating the original flavor of a food and exhibiting composite functions.
The present inventors halve developed a method for producing an aroma aqueous solution component which comprises indirectly heating a mixture consisting of fresh coffee beans, aracha (coarse tea leaves), cacao and shell in a stream of a mixed gas comprising an inert gas and superheated steam [refer to JP-A-61-70944, JP-A-6-119140, and JP-B-61-108351, the term "JP-B" as used herein means an "examined Japanese patent publication"] and conducted extensive studies on a substance capable of expressing a full-bodied flavor in this method. As a result, they have found that the compound as mentioned above has functions of imparting a full-bodied flavor, modifying sourness and/or saltiness and promoting the volatilization of an aroma thereof, thus completing the present invention.